Source: mythtv.org
There are four types of interfaces that are most commonly used these days. These interface are:
Bear in mind that a drive's performance as a video source depends on the 'sustained transfer rate' of the drive which has nothing to do with the interface type or speed. The sustained transfer rate is limited by the 'media transfer rate'. The media transfer rate is the rate of data transfer between the head and the disc surfaces. It is a physical limitation that is shared by all hard drives regardless of the interface. The only things that affect it are: the data density on the disc, the physical size (read/write area) of the heads, and the rotational speed of the drive. All drives with the same rotational speed and data density will have approximately the same media transfer rate. A high end 7200 RPM drive can achieve a max media transfer rate of approximately 80 MB/sec regardless of the interface being SATA, PATA, or SCSI. - Drive manufacturers don't want you to know this and divert attention from it by emphasizing the interface's speed in their ads. The interface's speed is only an advantage during data bursts. Most manufacturers went so far as to stop listing the media transfer rates in their specification tables. - With drive of a given rotational velocity and data density, the only way to improve overall system performance is to use a form of RAID that uses Stripping. This effectively uses two drives simultaneously so that the total media transfer rate is doubled.
(P)ATA
As a much older standard, PATA is universally supported on most x86 hardware. This interface was originally called ATA but when Serial ATA (SATA) was introduced it was renamed Parallel ATA. Recently, this function on motherboards has been shifted to a 3rd party controller, and boards only offer one port (two drives).
SATA
Most new hard drives and motherboards come with support for the newer Serial ATA (SATA) interface. Although SATA is a superior standard (it supports a lot of the SCSI subset, and features much smaller, thinner cables than PATA, amongst other improvements), some SATA controllers have closed-source or no Linux drivers. This has resulted in some Linux-based systems being unable to use SATA adequately due to poorly functioning controllers. This situation is no longer as serious as it once was, but you should check your hardware driver support to be sure.
For the current status of SATA support under Linux you can check Serial ATA (SATA) on Linux.
Please bear in mind that the built-in software RAID functions on SATA chips will usually not work in Linux without extensive fooling around with the kernel (if at all). Because Linux provides its own software RAID features, this isn't a big loss for a dedicated Linux box (such as a MythTV system), but if you dual-boot, you may not be able to use the controller's software RAID.
SCSI
SCSI stands for Small Computer Systems Interface, and is/was a competing hard drive interface to IDE/ATA. However, back in the mists of time, SCSI was designated to the "high end hard drive" side of things, and is now much more expensive than ATA technology. Though, if you look at things like raw drive MTBF hours, you will see that cheaper ATA drives are only now barely catching up to the SCSI drive specs.
None but the highest end server and workstation motherboards come with built-in SCSI host adapters, so these usually have to be added by means of a PCI card, which in themselves are not cheap. The cost of the hard drives are very high indeed, and they offer much reduced storage capacity compared to a modern PATA or SATA drive. However, SCSI disks are incredibly fast and very reliable -- but as we can see, it comes at a huge price. To be honest, there is very little chance of even an extensive MythTV setup requiring a SCSI system -- SCSI excels in massive multi-user environments like databases and web/mail servers, but the advantages under a single user setup are hard to distinguish. With the recent addition of Western Digital's enterprise-class "Raptor" SATA drives, you can approach SCSI speeds without shelling out a kings ransom, although their size is limited to 74GB at the time of writing.
One thing of note is that SCSI drives are very very loud due to their very high rotation speed (10,000 or 15,000rpm) and so are going to be relegated to the backend under the stairs pretty quickly. Raptor drives are quieter, but still far louder than your average IDE drive.
[ Editorial comment: SCSI's not that bad a choice, particularly if you can get used drives cheaply on eBay, and you are building an Under The Stairs backend box -- instead of the 2 or 4 drives you can put on most IDE controllers, you can put 15 on a SCSI controller -- and multiple channel controllers are available. So it is a matter of scale and buying savvy as much as anything else. -- Bay Link(2004-10-01T18:06:44Z)
SAS
SAS, or Serial Attached SCSI, is a new technology that takes the best of SCSI and SATA and in many ways it compares to Fiber Channel (e.g. SAN technology) and USB as well. Most modern servers already ship with SAS instead of SCSI, and they're eventually expected to be the desktop standard. As of today it has a bus bandwidth if 3 Gbps, and is on target to increase to 12 Gbps by 2011. Individual SAS drives today have a transfer rate of 300 MB/sec, just under the SCSI rate of 320 MB/sec, but each drive gets the full 300 MB/sec to the host, instead of shared as with SCSI, SATA and PATA. Current benchmarks show comparable performance to the best 15K Ultra320 SCSI drives and in some areas SAS far surpasses SCSI performance. Some other cool features are:
- Seagate Barracuda ES2 Serial Attached SCSI one terabyte drives can be found for around $270 - maybe even $250. They spin at 7200 rpm. Not a bad choice for MythTV systems that are going to be always on. RedmondTux